3213 Midterm Flashcards
What is Attenuation(unit)
What is the formula
dB is a measure of attenuation
Attenuation = 10 x log10 (P2/ P1) [dB]
dB measurements in several points are additive/subtractive
formula for dBm, dBw
dBw = 10 x log10 (P/1W) unit of Watt
dBm = 10 x log10 (P/1mW) unit of milliWatt
they are units of power
What is Delay distortion
Why
Change in signal shape/form
Each signal comp has own propagation speed through medium, therefor different delays
What is noise
Unwanted signals that get generated elsewhere, cannot be predicted
Signal to noise Ratio (SNR) formula + units
And
(SNRdB or S/NdB )
Ratio of signal power to noise power
avg signal power / avg noise power (watts)
for SNR (decibels)
SNR(db) = 10log10*(SNR)
Analog vs Dig transmission (signal reproduction)
Analog: all continuous details must be reproduced accurately
Digital: Only discrete levels need to be reproduced
What is a lowpass channel
- range
- dedicated users
[0 - f1) // begins at f=0
dedicated to two devices
devices alternate in transmission
What is a bandpass channel?
[f1 - f2) // Does not begin at f=0
medium shared among multiple users
each pair of users get a portion of total bandwidth
digital trans pros/cons
pros: does not need to completely recover OG signal shape
thrfor long distance achievable
cons: digital signal theoretically needs f= [0-infinity)
Needs lowpass channel, upper lim can be relax if only using n harmonics
Data level vs Signal level
Data levels: bits used to represent data
Signal level: levels allowed in a signal
What is Unipolar
Line coding scheme
uses only 1 non-zero voltage lvl, and a 0 lvl
issues: DC comp present, lack of sync for long series
What is polar line coding
Line coding scheme
Uses two non-zero voltage levels to represent two data levels
1 pos, 1 neg
DC problem alleviated
Types of polar line coding? (4)
Nonreturn to Zero // NRZ (NRZ-level, NRZ-inversion)
Return to Zero // RZ
Manchester (Of type RZ)
Differential Manchester (Of type RZ)
What is Polar: NRZ
Nonreturn to zero (name)
NRZ-level: signal lvl represents bit (ex: 0=pos, 1=neg)
NRZ-inversion: inversion of voltage lvl represents bit 1, no voltage change represents bit 0
- long seq of 0 is a problem still, 1 is fine since a change of voltage occurs
What is Polar: RZ
Return to zero
0=neg volt, 1 = pos volt
Signal MUST return to zero midway each bit interval
Pros: perfect sync | cons: 2 signal changes to encode each bit, pulse rate = 2x rate of NRZ // More bandwidth req